Top Mount vs Front Mount vs Water to Air

So you have been thinking about getting an intercooler for your turbo-charged vehicle for awhile but have discovered that there’s a few options available to you. Everyone that you have spoken seems to know it all and tells you that this is better or that’s better. Sound familiar? What we will discuss herein is the types of coolers that are out there, in an unbias way, so that you can make up your own mind on what will suit you best.

Firstly, let’s make sure we have a good understanding of what an intercooler does.

Your vehicle has a turbo or supercharger. These two devices both compress the intake charge of air to a higher atmospheric level.

A byproduct of this compression of the intake charge is heat, and there’s nothing you can do about it. As heat is an energy it cannot be overcome, instead it has to be displaced. The best way of displacing this heat on an engine is an intercooler system. Basically, an intercooler is a heat exchanger. It exchanges thermal energy from one source to another and simply displaces heat.

So why do we need to get rid of this heat?

There are a few reasons why this heat is undesirable, but the main issue we will look at is performance and reliability of your engine as well as economy. As hot air is less dense than cold air, the amount of fuel you can atomise into hot air is considerably less than it would be if the air was cold (dense). For obvious reasons the amount of fuel/air mix entering your engine has a fair bit to do with performance of your engine. More fuel and air equals more power. The more power you gain and the more efficiently your engine is running means the less you squeeze the throttle to do the same amount of work. This simply means increased economy. That is why you have a turbo or supercharger fitted, to supply your engine with more air, for more power.

However, if the intake charge of air is not cooled down before it enters the engine, you will not be gaining the full benefits of your forced induction setup. Typically intake temperatures on a turbo vehicle that us running conservative boost (less than 1 bar) will skyrocket over 100 deg C. A general rule of thumb is about 8 deg C will equal 1 horse power. This explains in basic terms why you need to get rid of intake temperatures, and why you need an intercooler.

What types of coolers are there?

Let’s look at the two basic types of coolers that are on the market: the air to air and the water to air. Air to air coolers use a fresh supply of air to flow around the tubes of the cooler containing the compressed and heated intake air, thus removing or displacing heat. Water to air coolers work in exactly the same manner, but use water as a medium to displace the heat. This is where a lot of debate takes place, as some believe one is better than the other. It’s like the old saying that there’s horses for courses. This is exactly what we will look at, as there are different cooler systems for different applications.

Water to Air

One of the major benefits of water-to-air cooling is that water (being a lot more dense than air) is an ideal medium to displace heat. The down side of this is unless you have a constant supply of fresh cold water, (like the cooler systems you may see on speed boats) you will heat up your supply of water very quickly. Unless you want to run a very long garden hose to your vehicle on trips, the only way to achieve this is to run another significantly large heat exchanger (such as a radiator) to remove the heat from your cooling water. The size of this second heat exchanger needs to be quite large to cool the water to an ambient level.

The other reason people use water-to-air cooling is that the unit itself can be very compact. This however does raise some concern about the flow capabilities of the cooler. For example, the more tubes you have in the cooler for the charged air to flow through the better it will work. How is this so? Well for one, there is the outright flow capability of the cooler to supply your engine with enough air. This is important because you don’t want to starve your engine due to a cooler that’s too small and wont flow enough. Also, if your cooler is large enough to be able to supply your engine with more than enough air, the speed at which the charged air flowing through it will decrease. This in turn will give the hot charged air more time to exchange heat with the internal surface of the cooler, thus resulting in colder air.

In summary, a water-to-air cooler should only be used if you have very tight confines to run a cooler or you only do short trips (about a quarter-mile). However, it is still better than nothing. A lot of car manufacturers started using them in the late 80’s early 90”s but soon dropped then in favor of more efficient air-to-air units. Some manufacturers still use them if they have tight confines to work with.

Air to Air

Ok, so now we are onto the Air-to-Air coolers. These types of coolers have been the main stay as the popular choice in the performance /racing industry for decades, as well as OEM manufacturers. Having a constant supply of fresh cold air means they don’t suffer from the same problem as water-to-air, whichs heats up its recycled cooling medium. They are much more simple, without pumps or secondary heat exchangers. They also won’t leak cooling water into the intake system of your engine should they fail, avoiding any costly engine repairs. We will divide these types of coolers into two categories: Front Mount Intercoolers (FMIC) and Top Mount Intercoolers (TMIC).

Front Mount Intercoolers (FMIC)

The venerable front mount cooler is the most popular type of system employed today. A large cooler sits at the front of the vehicle for excellent air flow and pipe work leads back into the engine bay. It’s a hard setup to beat for optimal cooling of the intake charge while the vehicle is in motion. That is why it is employed so much in race vehicles that are constantly undergoing speed and endurance. With air flowing over the cooler at the rate the vehicle is travelling, it’s not hard to see why these are so effective. Many car manufacturers currently employ this type of system because of it effectiveness, so a lot of people will upgrade their standard FMIC for a higher flowing unit and release the full potentional of their engine.

The drawbacks of such a system is the amount of pipe work you have to put into your intake system to plumb the whole thing up. A front mount intercooler requires at least 2 meters of piping fitted to the intake side of your engine.

No matter what people tell you, this will without a doubt cause throttle lag. All that can be done is make sure you fit high flowing pipe work that will not restrict the pressurised air being fed to your motor. Any good quality kit will have large enough pipe work, with the least amount of joiners. Some manufacturers already have large enough pipe such as 100 series Toyota Landcruiser factory turbo diesels and Nissan GTR Skylines. They understand the need to have high flowing pipes when you increase the length of an intake tract. Just be sure you don’t limit your power by fitting restrictive coolers with small pipe work, they are a waste of time.

Another drawback with FMIC systems is they can have a tendency to put extra load on your vehicles cooling system; eg. radiators and air-conditioning condensers. Unless your vehicle is already fitted with a factory front mount where the manufacturer would have taken this into account, you should purchase a quality FMIC system that has been designed by people familiar with your vehicle, who can demonstrate that no overheating issues will occur. If you require a system for your four wheel drive, then go to an experienced 4X4 shop that specialises in intercoolers. If you require a FMIC system for a on-road performance vehicle, then go to somebody who specializes in this field. Its as plain as chalk and cheese, don’t mix the two up!

The other drawback to the FMIC system regarding airflow, is primarily a concern to the 4X4 segment and the serious off-roader. FMIC systems rely on a steady stream of fresh air coming from the front of the vehicle to cool them down. This is fine as long as you are moving at a reasonable speed, let’s say anything over 50km/h. For a good number of off road enthusiasts, that speed may be a little excessive for rock crawling and the like. Likewise, the position of the FMIC poses the risk of damage due to impact, so pipe work may be routed in protected positions to avoid damage or constructed from strong materials. Another problem that has been seen many times in the off-road environment is the front mount cooler being totally blocked with mud. This renders the cooler totally useless. Depending on what type of off-roading your into, bear in mind that if you require good power at low speeds maybe a FMIC isn’t the way to go.

Top Mount Intercoolers (TMIC)

As the name suggests, these intercoolers are mounted on top of the engine. The intercooler is fed a supply of fresh air by a scoop in the bonnet. They have none of the issues associated with lengthy pipe work (such as throttle lag) because they can be mounted directly in line with the intake system, from turbo to intake. TMIC systems are free from damage cause by off road enthusiasts because of the position of the mounting. There is no extra thermal load placed on an engines cooling system, and there is little chance of the pipework becoming blocked with mud.

TMIC systems are a popular choice for many car manufacturers because they can see the benefits of their simplicity and performance of this type of system. There are hardly any joining sections to fail, and they are mounted well-and-truly out of harm’s way.

One downfall of the TMIC system is that they too require a steady flow of air to keep them operating efficiently. This is done in the same way as a FMIC with the vehicle speed being a factor in the amount of air flow the cooler receives. Some OEM manufacturers have overcome this problem by the use of a fan on the underside of the cooler to maintain a steady flow of air, even at zero vehicle speed. Without a decent fan to pull a constant flow of air through the cooler, TMIC systems can suffer severe heat soak, caused by the heat of the engine. A FMIC will still suffer heat soak from radiated heat from the radiator at zero speeds, but not as much as a TMIC due to the fact that heat rises. With a good fan-assisted top mount, you have a cooler system that is hard to beat in the world of off road 4X4ing.

With a Quality TMIC system that has been designed with a good fan (say at least 700cfm) you would have the best off-road cooler combination. It's got all the benefits of a FMIC, without the downfalls. You have true cooling capacity at crawling speeds, instant throttle response because of minimal pipe work, and best of all it doesn’t recirculate its cooling medium. It’s getting fresh ambient air the whole time.

In Summary

If you’re a hard 4X4 nut who loves pushing the limit of your truck, then a quality fan assisted top mount is the only way to go. It has just too many benefits.

If you’re into some off roading but do a fair amount of highway/ high speed work or you own a performance vehicle then a quality front mount maybe your answer. Don't discount the top mount however, as it comes down to what you value more. Speak to a specialist in the field of your particular type of vehicle, they will be able to steer you in the right direction. There’s nothing wrong with ringing around.

Last of all, if you’re into quarter mile drag racing, or you just don’t have the room for a FMIC or TMIC, then maybe look at a water-to-air or dry ice cooler.

We hope that the information has assisted you in making the right choice for your vehicle. If you're still unsure about anything Intercooler related, feel free to contact us.